1. Field of the Invention
The present invention relates generally to reconfigurable, solid-state matrix arrays comprising multiple rows and columns of reconfigurable secondary mechanisms that are independently tuned.
More particularly, our invention relates to reconfigurable devices comprising multiple, solid-state mechanisms characterized by at least one voltage-varied parameter disposed within a flexible, multi-laminate film, which are suitable for use as ground surfaces, antennas, varactors, ferrotunable substrates, or other active or passive electronic mechanisms.
2. Description of the Prior Art
Active structures including multiple micro electromechanical systems (i.e., MEMS) are well known in the art. Successful MEMS structures employ a variety of actuators to precisely control the multiple circuit elements involved. The use of digital controllers, that address secondary components arranged in orderly columns and rows, is known as well. However, it is difficult to precisely control large, matrix arrays of MEMS actuators operating at extremely high frequencies in the gigahertz range or above. Microwave MEMS control applications have hitherto been problematical.
Existing power control approaches employing small charge packets offer certain advantages. Efficient power-to-mechanical force conversion is achievable, and very high resolution or accuracy may be realized. However, such designs are inherently gain-bandwidth limited, due to their reliance on small charge packets. From a practical viewpoint, such designs require extensive control circuitry commensurate with the number of devices (actuators) within the system. The complexity and size of wiring buss designs within known power distribution systems increase with actuator density, thereby causing electromagnetic interference, radio frequency interference, and capacitive loss problems. Circuit degradation from mutual coupling is another factor.
There has been considerable work in efforts to develop a number of antenna designs, including both microstrip and phased array, using switch elements. In particular, a number of designs have attempted to achieve such implementation using MEMS. Such ‘hard’ switching approaches have encountered some very significant obstacles with switching implementation especially with enabling functional MEMS devices that can operate at relatively high, microwave frequencies.
Low-cost, lightweight, thin antennas, especially phased microwave designs, require many separate elements that are arranged in an orderly geometric fashion. This requires large numbers of small and inexpensive antenna switches. In the past, switches that exhibit the appropriate microwave characteristics have been problematical. Although there has been limited success in using MEMS approaches to fabricated small RF switches, the switches demonstrated thus far are expensive and often have relatively poor radiation characteristics, especially above 1 Ghz.
Usually, the hard switching portion of the system is implemented “off” antenna, whereas the soft switch circuitry is more typically incorporated into the antenna itself so as to reduce trace lengths, match impedances and impart flexible or conformal designs. The actual fabrication techniques can include lithography, microcircuit materials such as high temperature co-fired ceramic (HTCC) or low temperature co-fired ceramic (LTCC), roll-to-roll printing and may include either only passive elements in its incorporation or active elements such as thin film transistors that are amenable to compatible integration with the antenna substrate materials and processes.
A typical matrix architecture controlled performance antenna might have hundreds, thousands, or even tens or hundreds of thousands of individual elements, each with a number of tuned elements to control local phase and impedance and interconnections with other antenna elements. Efficient and low-cost control of the large number of tuning elements is a key requirement for a typical pixelated antenna approach. Clearly, connecting wires directly between each tuning element and a control system is unwieldy for even a small number of elements and impractical for arrays with large numbers of elements.
Electrically conducting metallic ground planes have been successfully used for many years in the design of a wide variety of antenna systems. However, there are several major drawbacks associated with using conventional metallic ground planes for antenna applications. For example, horizontally polarized antennas, such as dipoles, ordinarily are spaced at least a quarter-wavelength above their ground plane to achieve optimal performance, and ground planes of this type to support surface waves, which are undesirable in many antenna applications. Recently the concept of an artificial magnetic conductor (AMC) ground plane was introduced as a means of mitigating many of the problems associated with the use of conventional electrically conducting ground planes.
The term artificial magnetic conductor (AMC) typically refers to a structure comprising a dielectric layer having a conducting sheet on one surface and a frequency selective surface (FSS) on the other surface. The FSS is typically an array of conducting patterns supported by a non-conducting surface (the surface of the dielectric layer).
An individual conducting pattern, repeated over the surface of the FSS, may be referred to as a unit cell of the FSS. Conventionally, the unit cell is repeated without variation over the FSS. Typically, the unit cell is a square shaped conducting patch repeated in a grid pattern, for example as described in U.S. Pat. No. 6,525,695 to McKinzie et al. However, more complex shapes are possible.
At a resonant frequency, the AMC behaves as a perfect magnetic conductor, and reflected electromagnetic waves are in phase with the incident electromagnetic waves. This effect is useful in increasing the radiated output energy of an antenna, as radiation emitted backwards from the antenna can be reflected in phase from an AMC backplane, and hence can contribute to the forward emitted radiation, as any interference will be constructive.
Conventional AMC technology is described by D. Sievenpiper, et al., IEEE Trans. Microwave Theory Tech., vol. MTT-47, pp. 2059–2074, November 1999 and F. Yang, et al., pp. 1509–1514, August 1999. Thin AMC ground planes with thicknesses on the order of 1/100  or less of the electromagnetic wavelength can be effectively used to design low-profile horizontally polarized dipole antennas. The use of an AMC in this case allows the antenna height to be considerably reduced to the point where it is nearly on top of the AMC surface. In addition, AMC ground planes also possess the added advantage of being able to suppress undesirable surface waves.
While the conventional AMC ground planes can enhance the performance of many commonly used antennas, they are typically narrow band and lack the flexibility required for use in low-profile, frequency-agile antenna systems.
U.S. Pat. No. 6,483,480 to Sievenpiper et al. describes a tunable impedance surface having a ground plane and two arrays of elements, the one array moveable relative to the other. Int. Pat. Pub. No. WO94/00892 and GB Pat. No. 2,253,519, both to Vardaxoglou, describe a reconfigurable frequency selective surface in which a first array of elements is displaced relative to a second array. U.S. Pat. No. 6,690,327 to McKinzie et al. describes a mechanically reconfigurable AMC. However, mechanical reconfiguration of an array of elements can be difficult to implement.
U.S. Pat. No. 6,469,677 to Schaffner et al. describes the use of micro-electromechanical system (MEMS) switches within a reconfigurable antenna. U.S. Pat. No. 6,417,807 to Hsu et al. and U.S. Pat. No. 6,307,519 to Livingston et al. also describe MEMS switches within an antenna. U.S. Pat. No. 6,448,936 to Kopf et al. describes a reconfigurable resonant cavity with frequency selective surfaces and shorting posts. However, these patents are not directed towards a reconfigurable AMC.
U.S. Pat. No. 6,525,695 and U.S. Pat. App. Pub. No. 2002/0167456, both to McKinzie, describe a reconfigurable AMC having voltage controlled capacitors with a coplanar resistive biasing network. U.S. Pat. No. 6,512,494 to Diaz et al. describes multi-resonant high-impedance electromagnetic surfaces, for example for use in an AMC. Int. Pat. Pub. No. WO02/089256 to McKinzie et al., U.S. Pat. App. Pub. No. 2003/0112186 to Sanchez et al., and U.S. Pat. App. Pub. No. 2002/0167457 to McKinzie et al. describe the control of the sheet capacitance of a reconfigurable AMC. U.S. Pat. No. 6,028,692 to Rhoads et al. describes a tunable surface filter having a controllable element having an end-stub.
Approaches described in the prior art may allow the tuning of a resonant frequency of an AMC, but may not allow the change of other parameters such as resonance width, or allow reconfiguration of multiple band AMCs. Typically, adjustments are made over the whole surface of the AMC, not allowing for local adjustments. Also, reconfigurable antenna and digital matrix control architecture with single source supply are not disclosed.
Patents and published U.S. patent applications referenced in this application are incorporated herein by reference. Co-pending U.S. patent applications to one or more of the present inventors are also incorporated herein by reference, including: U.S. application Ser. No. 10/755,539, filed Jan. 12, 2004, to Werner (concerning metaferrite properties of an AMC); and U.S. application Ser. No. 10/712,666 filed Nov. 13, 2003 to Jackson concerning a reconfigurable pixelated antenna system.
What is required is reconfigurable, solid-state matrix arrays comprising multiple rows and columns of reconfigurable secondary mechanisms that are independently tuned.